Dust up in climate modeling

New information on the role of insoluble dust particles in forming cloud droplets could improve the accuracy of regional climate models, especially in areas of the world that have significant amounts of mineral aerosols in the atmosphere. A more accurate accounting for the role of these particles could also have implications for global climate models.

Cloud properties can have a significant impact on climate, yet the effects of aerosols like dust is one of the more uncertain components of climate change models. Scientists have long recognized the importance of soluble particles, such as sea salt and sulfates, in creating the droplets that form clouds and lead to precipitation. But until now, the role of insoluble particles – mostly dust swept into the atmosphere from such sources as deserts – hasn’t figured significantly in climate models.

Using a combination of physics-based theory and laboratory measurement of droplet formation, researchers at the Georgia Institute of Technology have developed a model that can be added to existing regional and global climate simulations. The impacts of these refinements on cloud condensation nuclei (CCN) activity and droplet activation kinetics are still being studied.

IMAGE: Georgia Tech professors Irina Sokolik and Athanasios Nenes hold samples of mineral dust they studied as part of research into the role played by insoluble dust particles in the formation…

“Understanding that insoluble dust forms more droplets than we thought it could, and that those droplets form close to the sources of the particles, could change our picture of how precipitation is formed in areas like the Mediterranean, Asia and other climate-stressed regions,” said Athanasios Nenes, a professor in the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology.

The research was supported by the National Science Foundation (NSF), the National Oceanic and Atmospheric Administration (NOAA) and NASA. The findings were described at the Fall 2011 meeting of the American Chemical Society in Denver, and reported in the journals Geophysical Research Letters, Journal of Geophysical Research and Atmospheric Chemistry and Physics. A new paper on the global modeling impacts has been accepted for publication by the Journal of Geophysical Research.

Soluble particles nucleate droplets by absorbing water under conditions of high humidity. Insoluble materials such as dust cannot absorb water, so it was thought that they played little role in the formation of clouds and precipitation.

However, Nenes and collaborators realized that these dust particles could nucleate droplets in a different way – by adsorbing moisture onto their surfaces, much as moisture condenses on window glass during temperature changes. Some insoluble particles containing clay materials may also adsorb moisture, even though they don’t dissolve in it.

Working with Irina Sokolik, also a professor in the School of Earth and Atmospheric Sciences, Nenes and graduate student Prashant Kumar studied aerosol particles created from samples of desert soils from several areas of the world, including Northern Africa, East Asia/China and North America. In laboratory conditions simulating those of a saturated atmosphere, these insoluble particles formed cloud droplets, though the process was slower than the one producing droplets from soluble materials.

“We generated particles in the

IMAGE: Containers hold samples of mineral dust studied by Georgia Tech scientists as part of research into the role played by insoluble dust particles in the formation of cloud droplets.

laboratory from materials we find in the atmosphere,” explained Nenes, who also holds a faculty appointment in Georgia Tech’s School of Chemical and Biomolecular Engineering. “These particles take up water using a mechanism that had not been considered before in models. It turns out that this process of adsorption soaks up enough water to form cloud droplets.”

The laboratory work showed that smaller particles were more likely than expected to generate droplets, and that their effectiveness as cloud condensation nuclei was affected by the type of minerals present, their size, morphology and processes affecting them in the atmosphere. The dust particles ranged in size from 100 nanometers up to a few microns.

These mineral aerosols may consist of iron oxides, carbonates, quartz and clays. They mainly originate from arid and semi-arid regions, and can remain suspended in the atmosphere for as long as several weeks, allowing them to be transported long distances from their original sources. In the atmosphere, the dust particles tend to accumulate soluble materials as they age.

“We can simulate what is happening to the particles as they get slowly coated with more and more soluble materials,” said Nenes. “As they get more and more soluble coatings on them, they become more hygroscopic.”

The researchers are now working with collaborators in Germany to incorporate their new theories into existing climate models to see how they may change the predictions. They also hope to carry out new field work to measure the activity of these insoluble aerosols in real-world conditions.

“We now need to study the cloud particles in the atmosphere and their ability to form droplets to verify our theory using real atmospheric data,” Nenes said. “We also need to look at dust and clouds from more regions of the world to make sure that the theory works for all of them.”

Clouds play an important role in governing climate, so adding new information about their formation could improve the accuracy of complex climate models.

“The reason that we care about particle-cloud interactions is that they introduce a lot of uncertainties in climate model predictions,” Nenes said. “Anything that can be done to improve these predictions by providing more specific cloud information would be helpful to projecting climate change.”

42 thoughts on “Dust up in climate modeling”

I can see that Climate Models will increasingly include a great many variables that actually do affect the weather, over and above trace gases. Although this at first may seem like a Good Thing, I will bet my bottom dollar that each and every new variable will be ‘tweaked’ at some point to prove that CO2 is the bringer of doom.

“The U.S. Environmental Protection Agency is considering a crackdown on farm dust, so senators have signed a letter addressing their concerns on the possible regulations.

The letter dated July 23 [2010] to the EPA states, “If approved, would establish the most stringent and unparalleled regulation of dust in our nation’s history.” It further states, “We respect efforts for a clean and healthy environment, but not at the expense of common sense. These identified levels will be extremely burdensome for farmers and livestock producers to attain. Whether its livestock kicking up dust, soybeans being combined on a dry day in the fall, or driving a car down the gravel road, dust is a naturally occurring event.”…..

I wonder if this study will give the EPA the ammunition to take another crack at “Farm Dust”

Mineral particles on their own are not very good at nucleating clouds, but they could be good receptors for other materials in the atmosphere. Ionizing radiation (cosmic rays) can produce lots of radicals and some of these when adsorbed on dustparticals could produce quite a reactive surface.

Silica is an excellent substrate in surface chemistry applications where surfaces can catalyze reactions that would not otherwise take place. Adsorbed ions on the surface could make the dust particles very hydrophilic resulting in spontaneous wetting by water molecules and rapid growth of droplets leading to cloud nucleation.

Some clays can contain layers of water and and therefore some hydrophilic surfaces would already exist. I understand that high concentrations of dust can be found throughout the atmosphere and therefore for me it has always been a strong candidate for cloud nucleation. The dust particles can be quite large so adsorbed water can easily achieve the critical droplet size for cloud formation.

Oh those scientists and their wacky theories… Why do they always have to explain that what they previously thought was wrong (already know that, thanks for the conformation), it’s probably the most frequent phrase in scientific journals, “… than we previously thought”.

I know particles can seed clouds, but there must be a lot more to it than that.

Australia is a dusty country. It’s not uncommon for the morning sky to be orange from dust, and the evening be a deep dust layer thick enough to blanket the sunset. Yet it goes weeks and months in drought conditions with barely a cloud in the sky.

Can someone answer a serious if maybe naive question? Are there incipient clouds hanging around everywhere waiting for a little dust or aerosol or cosmic ray or whatever the flavour of the month is, to form on? Does the lack of those things mean clouds do not form? Or is it the other way round, the dust is hanging around waiting for the right bit of water vapour to come along?

Is it not really the case that if a cloud wants to form, it will manage to, somehow?

“Insoluble materials such as dust cannot absorb water, so it was thought assumed that they played little role in the formation of clouds and precipitation.”

Now that’s the way it should have read … gotta watch those assumptions. IIRC, it was dust from the Sahara that was blamed one year for lessening the number of tropical storms/hurricanes in the Atlantic.

I know particles can seed clouds, but there must be a lot more to it than that.

Australia is a dusty country. It’s not uncommon for the morning sky to be orange from dust, and the evening be a deep dust layer thick enough to blanket the sunset. Yet it goes weeks and months in drought conditions with barely a cloud in the sky.

You can have too much of anything including seeding materials for droplet formation. If there are too many particles competing for a limited amount of water vapor it can make it so that none of the “seeds” gets enough droplet size to begin to form clouds or rain.

“Soluble particles nucleate droplets by absorbing water under conditions of high humidity. Insoluble materials such as dust cannot absorb water, so it was thought that they played little role in the formation of clouds and precipitation.

However, Nenes and collaborators realized that these dust particles could nucleate droplets in a different way – by adsorbing moisture onto their surfaces, much as moisture condenses on window glass during temperature changes. Some insoluble particles containing clay materials may also adsorb moisture, even though they don’t dissolve in it.”

What??! This becomes more and more ludicrous, that what traditional science has been teaching and still teaches at junior level is all so new to them..

How are clouds formed?
All air contains water, but near the ground it is usually in the form of an invisible gas called water vapor. When warm air rises, it expands and cools. Cool air can’t hold as much water vapor as warm air, so some of the vapor condenses onto tiny pieces of dust that are floating in the air and forms a tiny droplet around each dust particle. When billions of these droplets come together they become a visible cloud.

How come they don’t know this at University level? And it got supported and published by these science heavy-weights?

Thanks hotrod (Larry L). That’s not something I would have considered.

Re kalsel3294. I know moisture must be present, but there must be more to it yet.
I know nothing about the mechanics of droughts, or how they are maintained for so long, or what triggers their final demise back into rain. But I just can’t see something so simple as lack of moisture being the sum total (else it would never stop raining [all the moisture and all]).

Still, I don’t think has made the modelling easier, nor more reliable, for their efforts. But I’m glad they are able to quantify what they have learned.

Good grief, I figured this out years ago. Maybe it is because I lived most of my life near palouse soil. This is the kind of soil that generates dust storm warnings across freeways and have at times led to multiple car accidents and death. It is also the kind of dust that leads to cloudless rain. Dust is a staple of Earth’s life cycle. It is a food chain item. As important to life as air and carbon dioxide.

Anopheles says:
October 13, 2011 at 3:53 pm
Can someone answer a serious if maybe naive question? Are there incipient clouds hanging around everywhere waiting for a little dust or aerosol or cosmic ray or whatever the flavour of the month is, to form on? Does the lack of those things mean clouds do not form? Or is it the other way round, the dust is hanging around waiting for the right bit of water vapour to come along?

Is it not really the case that if a cloud wants to form, it will manage to, somehow?

Yes there are volumes of atmosphere that are supersaturated with water vapor and clouds may be triggered by dust or galactic cosmic rays that otherwise may not have formed.

Although this of course cannot be the case as we are told by Dessler and his supporters that clouds ONLY form as a feedback to temperature changes. Perhaps Dessler needs to get out of the computer lab and have a chat with a weather man and perhaps with Georgia Tech.

So they did a series of laboratory experiments showing that various dust particles can nucleate water droplets for cloud formation and precipitation, created an “add on” computer model to supplement existing computer models with the new information…

Did anyone go outside and capture some rain to see what’s in it? Or maybe some air samples from clouds goodness knows we’ve got all manner of weather baloons, rockets, airplanes and so on that could easily scoop some of cloud water droplets up so we could see what is in them. wouldn’t that have been SOOOOOO much easier? Not to mention ACCURATE?

But no…lab experiments, computer models…then right out to press yapping about the improved accuracy of the models. No need to sample actual water droplets for verification, the models trump reality anyway. Just ask Wolfgang Wagner….you could lose your job talking about reality!

Greg Cavanagh : October 13, 2011 at 5:31 pm.
Greg, understanding the mechanics and physics of droughts is one thing, but I believe it is more about understanding the logistics involved.
In Australia, there is nearly always a drought somewhere, and it never rains everywhere all at once. Just as what a El-Nino brings to one region, it is a La-Nina that brings the same to another.
I think there is too much attention being paid by the experts to the physics involved and not enough to understanding the logistics involved in the transport of water vapour.

i remember taking a Rudiments of Meteorology class in 1964 and the thought then was that particles in the atmosphere were initiation sites for water droplets to form. Here we are again. How disappointing.

North American prairie nomads knew how to induce rainfall from clouds by setting fire to the grasslands at exactly the right moment. This effect can easily be seen today above sugar cane fields that burn the trash before harvesting, for example in Swaziland and KZN in South Africa. Biomass PM makes it rain.

Anopheles,
According to the Svensmark hypothesis, cosmic rays seed the formation of low clouds, so there should be a reduction in the Earth’s low cloud cover in the aftermath of a Forbush decrease.
He found such a reduction in 2009.

So how do electrostatic dust separators work, why do (CRT type) TVs and monitors fill up with fluff and what is water if not a electro-sensitive (polar) molecule prone to splitting into hydroxide and hydromium ions?

I wonder if there’s anything else really tricky they’ve missed out such as… I dunno….fish can swim maybe or birds can fly possibly. Bet the computer says otherwise though.

Oh! Oh! I have a good one for them to study! And I am sure NO one knows this so don’t bother with a literature review (like that would happen otherwise). Why do steelhead and salmon ignore my fish hook? Now that is something I really don’t know and would pay to know the answer!!!

As for the diligently researched and announced teleconnections between dust, clouds, and rain, yaaawwwnnn. Know that, try again kids.

Pamela;
Don’t handle your lures and bait until you’ve fondled a fish; someone else’s will do till you catch your own first one. Fish obviously don’t like your smell, so you have to make your hands smell fishy first.

(I dare you to suggest an alternate method. I’m not going there … >;-) )

This summer, during the flurry of wildfires in Oklahoma, Texas, and Louisiana my family and I were driving south on the Turnpike between Tulsa and Hugo. There was one large fire that, as the smoke rose into low scattered clouds (“fair weather clouds”), was then pouring rain out less than a mile to the east of the fire from the only large dark cloud anywhere to be seen. There was no rain elsewhere to the horizon.

Well it is well known that a water droplet MUST contain a higher internal pressure than its surrounding ambient pressure; because of surface tension trying to crush the drop of water.
That excess internal pressure is trivially calculated to be 2 t/r, where t is the surface tension in Newtons per metre, and r is the surface radiaus of curvature in metres.

So a forming water droplet, must presumably start at near zero radius, when two water molecules meet up so the internal pressure would need to be near infinite.

Now the water droplet can form a ta larger than zero radius, if it has a huge dust particle to land on and start the droplet at some large radius. Doesn’t need to react with the dust particle in any way; the particle simply establishes a maximum surface curvature that the water needs to adapt to.

So there might be all sorts of fancy theories about some chemical surfactant effect that requires the presence of some sulphuric acid or somesuch “aerosol”. I like the simple geometry situation description myself.

Same thing happens when water tries to boil in the bulk; the steam bubble must have an internal excess vapor pressure of 2t/r so it too doesn’t like to form at 100 deg C, so it tends to superheat to a higher than boiling temperature, until some cosmetic ray or dandruff spec falls in the pot, causing explosive formation of a steam bubble around the particle..

Is Camelot the fairytale Al Gore and the IPCC think they can make come true?
It’s true! it’s true! The crown has made it clear,
The climate must be perfect all the year.
A law was made a distant moon ago here, July and August cannot be too hot.
And there’s a legal limit to the snow here, on planet Earth
The winter is forbidden till December, and exits March the 2nd on the dot.
By order, summer lingers through September, on planet Earth.
Planet Earth! Planet Earth!
The rain may never fall till after sundown. By eight the morning fog must disappear.
On short there’s simply not a more congenial spot,
For happily ever after aftering than here on planet Earth!
Heh heh! Heh!